Many approaches have been used to contain or isolate pollutants to limit contamination of soil and ground water. This problem is particularly acute where hazardous waste is stored in ponds or drums. Conventional technology in the field involves placing liners made of clay, cement, or plastic around and under the pond or drums to control seepage of pollutants into the surrounding soil and ground water. This approach is suitable where a liner can be installed before pollutants are released. However, liners have limited usefulness in situations where a release of pollutants has previously occurred. In the case of the Lowry landfill near Denver, Colo, pollutants have seeped to a vertical depth of several hundred feet below the earth's surface and contaminated ground water aquifers. Similar situations exist at a number of other hazardous waste sites. The available remedies in these cases are generally limited to excavation of the contaminated soil or treatment of pollutants by means of chemical, solvent, or biological techniques.
Chemical grouting has long been used in a variety of applications to control migration or flow of fluids. Cement or polymeric grouts have long been used in the oil industry and in in-situ leaching of minerals to control migration of oil, natural gas, and ground water, and to prevent the escape of lixiviants, solvents, or working fluids into surrounding formations. In applications of this type, a grout curtain is formed by drilling a series of closely-spaced wells in which grouting material is injected under pressure. For example, polymeric grouting was used to decrease the permeability of a natural formation in the course of constructing the Rocky Reach Hydroelectric Project in Wenatchee, Wash., in the late 1950's. Similar grout curtains have been used to prevent leakage from cooling ponds at power plants. Several examples of these types of application are provided in R. H. Karol, Chemical Grouting, (Marcel Dekker, Inc. 1983).
In the field of in-situ mining, directional drilling combined with hydraulic fracturing has been used in the past to encapsulate the ore body. For example, Lyons, et al., U.S. Pat. No. 4,311,340, "Uranium Leaching Process and Insitu Mining," issued Jan. 19, 1982, teaches that hydraulic fracturing of boreholes may be employed to create cracks and passage ways in the strata surrounding the boreholes to facilitate greater penetration of the grout or other impermeable materials (columns 7-8). Lyons also discloses that organic polymers and epoxy resins, as well as a wide variety of other materials can be used to create this impermeable barrier. The primary limitation of this approach is the manner in which horizontal barriers are formed above and below the ore body. Lyons relies on slanted boreholes formed by directional drilling for this purpose, as shown in FIGS. 5-11. While this technique may be effective for a relatively small geological formation or aquifer, it quickly becomes impractical when dealing with a large formation, particularly one having a large horizontal cross section. In such cases, a radial arrangement of slanted boreholes does not result in a uniform degree of encapsulation due to radial diversion of the boreholes. Directional drilling also entails additional costs.
In contrast, the present invention overcomes these shortcomings by using a grid of vertical boreholes to create an overlapping grid of horizontally-oriented fractures above and/or below the contaminated formation that is then injected with a cement or polymeric grout. In addition, a vertical grout curtain can be installed about the periphery of the contaminated formation to provide complete encapsulation. The grid of boreholes also provides a ready means for monitoring or treatment of the contaminated formation, or for removal of pollutants from the formation.